FURTHER STUDIES ON THE BIOLOGY OF PYRRHARCTIA (ISIA) ISABELLA (LEPIDOPTERA: ARCTIIDAE): III. THE RELATION BETWEEN HEAD CAPSULE WIDTH AND NUMBER OF INSTARS

Abstract

AbstractHead capsule widths of laboratory-reared and mature field-collected larvae of P. isabella were measured. The number of larval instars varied from 7 to 10, yet in all larvae studied, average size and increment in the successive instars were the same for instars 1 to 3. In the latter instars, there was an inverse relationship between size of increment and prospective number of instars. Insects which completed 10 instars were only a little larger than those maturing after only 7 instars. These data fail to support Dyar’s rule.